Cutting tool materials - Greetings from Eng....
Transcript of Cutting tool materials - Greetings from Eng....
Cutting Tool MaterialsEng R. L. Nkumbwa
Copperbelt University2010
Eng Nkumbwa 2010 2
History of Cutting Tool Materials
• Cutting tool used during the industrial revolution in 1800 A.D
• First cutting tool was cast using crucible method (1740) and slight hardened by H.T.
• 1868: R. Mushet found by adding Tungsten we can increase hardness and tool life ( Air Quenching)
Eng Nkumbwa 2010 3
History of Cutting tools• F.W.Taylor in Pennsylvania did the most basic
research in metal cutting between 1880-1905– Invented high speed steel (better H.T. process)– Better alloy
• Tungsten Carbide was first synthesized in 1890.• Took 3 decades before we got Cemented
carbide• First used in Germany • Sintering technology was invented
Eng Nkumbwa 2010 4
Cutting tool materials
• Selection of cutting tool materials is very important
• What properties should cutting tools have?– Hardness at elevated temperatures– Toughness so that impact forces on the tool
can be taken– Wear resistance– Chemical stability
Eng Nkumbwa 2010 5
Types of Tool Materialso Carbon + medium alloy steelo High Speed Steel (HSS)o Cast cobalt alloyso Carbideso Coated toolso Ceramicso Cubic boron nitride
o invented by GE in 1969o Silicon Nitrideo Diamond
Eng Nkumbwa 2010 6
High Speed Steel (HSS)• Early 1900s • Very highly used alloy steel• Can be hardened to various depths• Good wear resistance• High toughness• Good for positive rake angle tools.• Two basic types of HSS
– Molybdenum: ( M Series)– Tungsten: (T Series)
Eng Nkumbwa 2010 7
High Speed SteelT Series• 12 – 18 % Tungsten• Chromium, Vanadium etc.M Series
– 10% Molybdenum– Chromium, Vanadium, Tungsten, Cobalt– Better abrasion resistance– Less expensive– Less distortion– 95% of HSS used is M series
Eng Nkumbwa 2010 8
High Speed Steel
Manufacturing• Cast• Powder MetallurgyApplications• Taps• Gear cutters• Drills
Eng Nkumbwa 2010 9
Cast Cobalt (Stellite Tool)• 38 – 53% Cobalt• 30 – 33% Chromium• 10 – 20 % Tungsten• High hardness (58-64 HRC)• Good wear resistance• High temperature hardness• No Toughness
– not suitable for intermittent cutting• Good for deep boring, continuous turning• ( better than HSS)
Eng Nkumbwa 2010 10
Carbides• Most HSS and Cast Alloy have very low “high
temperature” hardness• Low life for high speed machining• Carbides
– High temp Hardness– Low thermal expansion– High modulus of elasticity
Tungsten Carbide (W-C)• Used for cutting non ferrous abrasive and metal + cast
iron• Tungsten Carbide particles are bonded in Cobalt matrix
Eng Nkumbwa 2010 11
Cermet (Titanium Carbide)• Invented in 1950 • Used since 1970Coated Carbide• Made of WC – Co – TiC - TiN• 3 – 4 coatings of Al2O3
Eng Nkumbwa 2010 12
• Particles sized 1- 5 mm are pressed and sintered into desired shapes (% of Co may vary)
• W-C is also compounded, sometimes with Titanium and Tantalum to improve hot hardness and crater wear
Titanium Carbide• Ti-C has Ni-Mb matrix• Good wear resistance and poor toughness• Good for machining steel • Higher speed than W-C
Eng Nkumbwa 2010 13
• Stiffness of the machine is important• Low feed, low speed and chatter can cause
failureCarbide Inserts• Smaller angle has less strengthCoated toolsThe coating is 5-10 mm in thickness
• http://www.carbidedepot.com/bbars.asp
Eng Nkumbwa 2010 14
Titanium Nitride• Low friction • High hardness• Resistance to high temperature• Improves life of HSS, carbidesCeramics• High temperature resistance• Chemical inertness• Wear resistance• Al203
Eng Nkumbwa 2010 15
Ceramic Cutting Tool• Brittle• Nowadays used extensively
Eng Nkumbwa 2010 16
Ceramic• Fine grained , high purity Al203 cold pressed at high
temperature and sintered at high temperature (white)Cermets• 70% Al203 30 % T-C• Very high temperature hardness• High abrasion resistance• More chemical stability• Less tendency for adhesion so less BUE• Good surface finish while machining steel and CI• Poor toughness for intermittent cutting
Eng Nkumbwa 2010 17
Cubic Boron Nitride• Next to diamond, the hardest material• 0.5-1mm polycrystalline cubic boron nitride• High wear resistance• But brittle• Used for machining hardened steel and
high temperature alloys ( Ni for instance)
Eng Nkumbwa 2010 18
Silicon Nitride• Used for super alloys
Diamond• Low friction and high wear resistance• Good cutting edge• Single crystal diamond are used to machine
copper to a high surface finish• Because they are brittle rake angle has to be
low
Eng Nkumbwa 2010 19
Polycrystalline diamond tool• (Compacted) synthesized crystals• Fused at high temperatures and high
pressures
Eng Nkumbwa 2010 20
Eng Nkumbwa 2010 21
Eng Nkumbwa 2010 22
Tool life curves for various tool materials in medium and light turning operations as a function of cutting speed. Note how the curve for ceramics crosses over the curve for T-C as speed , hence temperature, increases
Effect of cobalt content in T-C tools over mechanical properties. Hardness is directly related to compressive strength and hence, inversely, with wear
Eng Nkumbwa 2010 23
Relative time required to machine with various tool cutting materials, indicating the year the cutting tool material were first introduced
Eng Nkumbwa 2010 24
Property Carbon and low to medium alloy steels
HSS Cast Cobalt alloys
Cemented carbide
Coated carbide
Ceramics Poly -crystalline CBN
Diamond
Depth of cut
Light to medium
Light to heavy
Light to heavy
Light to heavy
Light to heavy
Light to heavy
Light to heavy
Very light for single crystal
Finish Obtainable
Rough Rough Rough Good Good Very good Very good excellent
Method of processing
Wrought Wrought, cast, HIP, sintering
Cast, HIP and sintering
Cold pressing and sintering
CVD Cold pressing and sintering
High pressure and high temp. sintering
High pressure and high temp sintering
Fabrication Machining and grinding
Machining and grinding
Grinding Grinding Grinding Grinding Grinding and polishing
Grinding and polishing
Eng Nkumbwa 2010 25
Property Carbon and low to medium alloy steels
HSS
Cast Cobalt alloys
Cemented carbide
Coated carbide
Ceramics Poly -Crystalline CBN
Diamond
Hot hardnessToughness
Wear resistanceChipping resistanceCutting speedThermal shock resistance
Total material cost
increasing
increasing
increasing
increasing
increasing
increasing
increasing